1. Field of the Invention
The present invention relates to a polyamide composition. The polyamide compositions of the present invention have excellent heat aging characteristics, as well as excellent mechanical characteristics, low-water-absorption properties and dimensional stability. The polyamide compositions of the present invention can be used as molding materials for industrial materials or the manufacture of household goods. The polyamide compositions of the present invention are, especially, suited for various articles, which is used at a high temperature, such as engine room parts of an automobile.
2. Description of the Background
Crystalline polyamides represented by nylon 6 and nylon 66 have been used widely in the manufacture of fibers for clothing and as industrial materials. The crystalline polyamides have also been used as general-purpose engineering plastics, because they have excellent thermal properties, physical properties and rigidity with good balance. Such general-purpose aliphatic polyamides exhibit undesirable properties such as insufficient heat resistance and poor dimensional stability because they absorb water. Particularly in recent years, polyamides which are intended for use in the fields of electrical and electronic parts, automobile parts, and fibers are required to have excellent heat aging characteristics.
In order to meet the above requirements, one approach has been to provide polyamide compositions comprising an aliphatic polyamide and a stabilizer such as (i) a copper salt, which is derived from the reaction of a copper halide and xylenediamine (U.S. Pat. No. 3,639,335), (ii) a copper phthalate and an alkali metal iodide (U.S. Pat. No. 3,457,325) or (iii) a mixture of copper, halogen- and phosphorus-containing compounds (U.S. Pat. No. 4,937,276).
Another approach to the problem is the preparation of polyamide compositions which comprise a semi-aromatic polyamide. The heat resistance of these polyamide compositions is generally better than that of an aliphatic golyamide, and the incorporation of a copper compound as a stabilizer into the compositions has also been proposed. U.S. Pat. No. 5,003,009 discloses impact resistant nylon molding materials containing (A) a linear, thermoplastic nylon composed of radicals derived from terephthalic acid, isophthalic acid and alkanediamines of 4 to 10 carbon atoms, and (B) one or more copolymers of (i) ethylene, an ester of (meth)acrylic acid and a monomer having an acidic functional group or a latent acidic functional group, or (ii) an ester of (meth)acrylic acid, a monomer having an acidic functional group or a latent acidic functional group and a monomer having 2 or more olefinic double bonds, and, if required, (c) effective amount of additives such as antioxidants and stabilizers, e.g. copper (I) halides. Japanese Patent Application Laid-open No. Hei 7-228768, (JPA 228768/95) discloses a polyamide composition comprising (a) a semiaromatic polyamide having (i) terephthalic acid units and 1,9-nonanediamine units or (ii) terephthalic acid units, 1,9-nonanediamine units and 2-methyl-1,8-octanediamine units, and having an intrinsic viscosity [η] measured in concentrated sulfuric acid at 30° C. of 0.4 to 3.0 dl/g, (b) a copper compound, (c) an alkali metal halide and (d) an organic stabilizer. Japanese Patent Application Laid-open No. Hei 7-228773 (JPA 228773/95) discloses a polyamide composition comprising (a) a semiaromatic polyamide having (i) terephthalic acid units and 1,9-nonanediamine units or (ii) terephthalic acid units, 1,9-nonanediamine units and 2-methyl-1,8-octanediamine units, and having an intrinsic viscosity [η] measured in concentrated sulfuric acid at 30° C. of 0.4 to 3.0 dl/g, (b) a copper compound and (c) a nucleating agent. U.S. Pat. No. 5,763,561 discloses an injection moldable composition comprising (a) a semiaromatic polyamide containing about 0 to about 40 μeq/g of carboxylic acid end groups, said polyamide containing aliphatic diamine units of 4 to 14 carbon atoms and terephthalic acid units; and (b) a copper-containing thermal stabilizer formulation comprising an alkali metal halide and a copper (I) halide in a weight ratio ranging from about 2.5:1 to about 20:1.
However, the present inventors have found that it is desired to improve the heat aging characteristics of the known polyamide compositions such as described above in order to meet the requirement of the excellent heat aging characteristics which are needed for, e.g., engine room parts of an automobile.